My Adventures in Satellite Communications - Part 7

Part 6 focussed on the patch antenna being used as the feed for the 80cm dish. In this part I describe the efforts I have made to improve the 2.4GHz transmit amplifier, originally described in part 1 and part 4. In particular I wanted to see if the power output could be increased.

Power Amplifier Modifications

My first problem is that I cannot measure the actual RF output, as I do not have a microwave power meter. However, I can measure the DC current drawn from the power supply, which gives an indication of output power. I found some data on the internet relating DC supply current of the EP-AB003 amplifier vs supply current ( Another crude way of evaluating improvements in uplink power is to monitor the downlink from the satellite.

Some radio amateurs claim that they have increased the gain and/or output power of the EP-AB003 amplifier by bypassing the Tx/Rx switching devices and reducing the voltage drop on the power PCB tracks (traces). I do not need the amplifier to switch between transmit and receive since I previously modified it to be stuck permanently in transmit mode. The photos show the mods I carried out. Bypassing the Tx/Rx switching device on the input side was very difficult to do and this put me off doing a similar mod on the output switching device.

Bypassing the Input Tx/Rx Switch with a Wire Link
Bypassing the Input Tx/Rx Switch with a Wire Link
The thick red wire reduces the voltage drop in the power rail
The thick red wire reduces the voltage drop in the power rail.

Unfortunately the modifications produced no measurable improvement in the amplifier performance.

Increasing the Gain of the Transmit Chain

The next question to answer was whether there was enough gain in the transmit chain to drive the EB-AB003 power amplifier to maximum output. The existing setup comprised of the ADALM Pluto SDR, followed by two cascaded SPF5189Z wideband amplifiers, a 2.4GHz bandpass filter, and finally the power amplifier. I decided against adding another SPF5189Z amplifier in the chain as this would result in the third amplifier being overdriven. So for the additional amplifier I went for a small 2.4GHz power amplifier, based on a RF2126 chip, capable of delivering up to 1W. The amplifier (shown in the photo) was quite cheap, but probably slightly over-engineered with its large integral heatsink. Certainly, with the 1W amplifier following the two wideband amplifiers I was able to overdrive the main power amplifier. Unfortunately, during the experiments I may have damaged the 2.4GHz bandpass filter, as it became a lot more lossy, so I removed it. With the power amplifier being driven harder there was no noticeable increase in the signal strength of the signal coming back from the satellite. I concluded that having three amplifiers between the Pluto SDR and the power amplifier was unnecessary, and probably undesirable from a signal quality point of view. I settled on just having the one SPF5189Z wideband amplifier followed by the 1W 2.4GHz amplifier, feeding directly into the main power amplifier. The 1W amplifier offers a lot more headroom than the 2nd wideband amplifier (the EDUP power amplifier typically needs several hundred milliwatts of drive to get full output) so should help prevent compression and distortion. For the moment I am not using a bandpass filter. I feel a little more comfortable with this now one of the wideband amplifiers has been replaced with a 2.4GHz amplifier with reduced bandwidth.This setup gives no less signal back from the satellite then when the power amplifier was being driven a lot harder.

The new 2.4GHz amplifier consumes a lot more current than the SPF5189Z, therefore I have had to upgrade the heatsinking on the 5V linear regulator.

Opened uplink amplifier showing the wideband amp and 1W power amp.


With maximum drive from the Pluto SDR, the amplifier system draws 1.655 A from a 12V supply. At this drive level the 1W amplifier draws 300mA. Allowing 75mA for the SPF5189Z amplifier, this implies the EB-AB003 power amplifier is drawing 1.28 A. I reckon this corresponds with an RF output power of around 2.5 Watts.


The modifications have not resulted in any measurable increase in RF output power. So has this all been a waste of time? I do not think so.
  • Sometimes it is worth recording the things that do not work well as well as the successes. This is how we learn!
  • I am now satisfied that I am getting as much power out of the EDUP EB-AB003 as is practically possible without overdriving it. 

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  1. maybe make yourself a power meter first because your approach is kind of ridiculous, measuring current increase of mainly class A amplifiers.
    If you would have a meter you would know the 1W ebay device is worthless only providing like 4dB gain like the ones I tested here.
    So my advice, first build a power meter and then go on AO100 with your Pluto.

    PS I use a single commercial class A module to gi from -10 dBm to 47 dBm. Bought it at a rally for 50 euros....

    1. Thanks for your comments.
      With these wifi power amplifiers the supply current will increase as power output increases, although I make no claim that this is a linear relationship. Therefore it gives a crude indication to compare different ways of driving the amplifier, i.e. finding which one gives the most drive. I agree the performance of these cheap Chinese amplifiers falls well short of the manufacturer's specs. A particular reason I used the 1W amplifier as it would be less likely to limit/compress at power levels needed at the input the the wifi power amp. I thought it was worth sharing my experiences as I know a lot of other experimenters are using the "8W" wifi amp in their QO-100 uplinks. I have gone as far as I can with this setup, so I either need to improve the antenna system or start again with a much better power amp. Sounds like you got a bargain with your amp! Yes, of course, using a decent microwave power meter would a lot more sensible, although quite expensive.

  2. AD8318 power meter is very cheap.
    You are a lecturer in electronics ? Really ?? You should know above circuit... :-)

    1. Yes - really!, but I have never used that particular chip before. Just checked it out and agree that it is cheap to buy an AD8318-based module for a few dollars. So, yes, it would not be difficult to make a microwave mW meter with it, with RF attenuators for measuring higher power. Thanks for the tip.

  3. i do like it when people say what you should get to test your set up.... in an ideal world we would all have everything but the real challenge is when you havnt got all the test stuff and how you work around the problem as best as you can and keep on learning

    1. Agree 100%. The main aim of the blog is to promote learning through encouraging experimentation and having fun with electronics and radio. Although I am an advocate of good technical education, it is difficult to 'teach' ingenuity in a classroom!

    2. Laurence. I just came across this thread via Google, searching the SPZ LNA. It’s interesting that Kure a lecturer and that others have commented in this. I too attempted the same circuit that your photo capture depicts and got nowhere too. I assumed that I was just getting it all wrong, that I just don’t what I’m doing, but glad to hear that th 1W amps are not what they are claimed to be. I even got the Chinese seller to tune the module to 2.4GHz for me, but to no avail. Not even sure that the SPZ component is genuine either, as many fakes around. Currently working on a complex network of video (w/audio) relay modules, trying my best to get the noise factors down to a bare mimimum. SPZ claims to have 0.6dB at the lower end, but there is a superior chip to all of these that came out last year, I believe, and has an extremely low noise figure. An amateur even created a functional and very professional circuit for that chip. Quora - not sure of the model. I was the one at school who sat at the back, got nowhere, considered dumb, with no prospect of getting anywhere in life. Funny how things turn out. Very much into sciences now and can take on the professors, for sure. MJ


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